The very large transition dipole moments of Rydberg atoms are responsible for strong long-range dipole-dipole interactions as well as very large couplings to external fields. Because of this property, Rydberg atoms have found direct applications for quantum sensing, quantum simulation, and non-linear optics at the few-photons level. I will describe a few examples realized in the Rydberg atom group at CQT.

In the first part of the talk, I will present our recent demonstration of coherent microwave-to-optical conversion via frequency mixing in Rydberg atoms [1]. In contrast to other physical systems being explored, our scheme requires no cavity and allows for free-space and broadband conversion due to the strong coupling of microwaves to Rydberg transitions. This result is promising for future quantum communication networks, as broadband interconversion of microwave and optical fields will be essential for connecting superconducting qubits and photonic qubits. I will discuss the recent strategies that we have developed for improving the efficiency of the conversion, which include the demonstration of three-photon electromagnetically induced transparency (EIT), and collinear frequency mixing [2,3].

In the second part, I will present our long-term goal of demonstrating spatially resolved imaging of Rydberg atoms, using Rydberg EIT in the presence of long-range dipole-dipole interactions. I will describe diverse characterizations of the effect of interactions on Rydberg electromagnetically induced transparency, and show that Lévy statistics describes well this many-body system [4,5].